Efficiency in the overall production of fluids and gases from a well is highly dependent on the effectiveness of production chemicals. Such production chemicals include completion fluids as well as treatment solutions for production stimulation. For example, aqueous acid solutions are often used to increase the permeability of a formation by injection of an aqueous acid solution into the formation so that mineral constituents are dissolved and flow channels are produced. In these methods, difficulties are often encountered due to water-in-oil emulsions (having crude oil deposits as the outer phase) which are formed downhole at the interfaces between the injected aqueous treating solutions and crude oil contained in the formations. Fines and insoluble reaction products which are formed accumulate at the oil-water interfaces and stabilize the emulsions which in turn tend to plug the pore spaces in the formations being treated, thereby restricting the flow of the treating solutions and subsequent production of fluids therethrough. While a variety of additives having surface active properties have been developed for preventing the formation of emulsions, sludge, etc., as well as preventing the corrosion of metal surfaces, and have been included in the various treating solutions employed, less than desirable results are often achieved.
In addition, and particularly where aqueous acid treating solutions are utilized, sludge formed as a result of the reaction of the acid with asphaltic materials contained in the crude oil can plug the pore spaces of the formations.
Other solid particulates are known to negatively impact the overall efficiency of completion of the well. These include asphaltene and paraffin deposits and scales, such solid particulates include residues from drilling muds. Commonly employed drilling muds are gaseous or liquid. Liquid drilling muds have a water base or an oil base. The aqueous phase of the more common water-base muds may be formed of fresh water, or, more typically, a brine. As a discontinuous or disperse phase, water-base fluids may contain gases or water-immiscible fluids, such as diesel oil, in the form of an oil-in-water emulsion, and solids including weighting materials, such as barite. Water-base fluids also typically contain clay minerals, polymers, and surfactants for achieving desired properties or functions.
Oil base fluids have a continuous phase based on synthetic or non-synthetic oil and, eventually, an aqueous phase dispersed in the oil phase. Oil-base drilling muds provide shale inhibition, lubrication, gauge hole, and higher rates of penetration and deeper bit penetration and therefore, may often be preferred over water-base muds. Oil-base muds are usually more difficult to remove however due to the hydrophobic nature of the mud.
Asphaltenes are most commonly defined as that portion of crude oil which is insoluble in heptane. Asphaltenes exist in the form of colloidal dispersions stabilized by other components in the crude oil. They are the most polar fraction of crude oil, and often will precipitate upon pressure, temperature, and compositional changes in the oil resulting from blending or other mechanical or physicochemical processing. Asphaltene precipitation occurs in pipelines, separators, and other equipment. Once deposited, asphaltenes present numerous problems for crude oil producers. For example, asphaltene deposits can plug downhole tubulars, wellbores, choke off pipes and interfere with the functioning of separator equipment.
Unwanted particulates not only cause a restriction in pore size in the rock formation (formation damage) and hence reduction in the rate of oil and/or gas production, but also cause blockage of tubular and pipe equipment during surface processing. It is well known that production efficiency increases if such unwanted solid particulates are removed from the wellbore.
To remove such particulates, the production well is generally subjected to shut-in, whereby compositions are injected into the production well, usually under pressure, and function to remove the unwanted particulates. Shut-ins need to be done regularly if high production rates are to be maintained and constitutes the down time when no production takes place. Over the year there is a reduction in total production corresponding to the number of down times during the shut-in operation.
Production is decreased when ineffective chemicals are used during shut-in. For instance, ineffective scale inhibitors fail to reduce total scale build-up. Poor displacement of drilling mud results in solid residues and mud residues left in the wellbore which, in turn, typically leads to formation damage, etc. Similar displacement or mud removal procedures are also performed before cementing. Mud residue can lead to weak bonding between cement and the formation surface and gas leakage when the well is turned to production.
The prior art has recognized the use of surfactants in the displacement and removal of oil base muds. Surfactants are first dissolved in fresh water or seawater at the concentration of 5 volume percent or more and the resulting liquid is then pumped at sufficient rate to generate turbulent flow to facilitate the mud cleaning process. Although surfactant systems have been widely used in field applications, their effectiveness is often limited by solvency capacity. In addition, the efficiency of surfactant systems varies for different muds and is negatively impacted by the condition of the mud when the displacement is conducted. Pure organic solvent is often effective in mud displacement process, especially in cases where surfactant systems are not effective. In most cases, due to strong solvency of the organic solvent toward the base oil in oil based mud, solvent has shown good mud removal and cleaning effects in both laboratory and field applications. However, pure organic solvent is generally expensive and, since it has been effective only when used in 100% pure form, it often becomes cost prohibitive. Although water can be mixed with organic solvent to cut the fluid cost, the effectiveness of the system can be greatly reduced, even at levels as low as 10to 20volume percent of water content. In other cases, especially when solid content in the mud or mud residue is high and the mud viscosity is significant, pure solvent is often not effective.
Organic solvents are further often used in formation cleanup or near wellbore damage removal when the damage is caused by asphaltene or paraffin deposition as well as scale deposition. Very often the solvents are aromatic and leave an environment footprint. In other cases, the solvent is not effective, especially when suspension and dispersion of solids is desired. Pure organic solvents cannot effectively break up solid aggregation and does not facilitate solid suspension.
Improved production chemicals are therefore desired for the treatment of fluid producing wells which are capable of removing or inhibiting the formation of unwanted particulates within the well. Accordingly, the present invention is a process for increasing the effectiveness of production chemicals by reducing the number and duration of shut-in operations needed to increase the production rate from an oil well.